1. Field of the Invention
The present invention relates to a water pump, and in particular, to a water pump used in the cooling system of an internal combustion engine on a vehicle.
2. Description of the Background Art
Various water pumps are known in which a cooling water discharge port is formed in the outer peripheral portion of an impeller adapted to rotate within a pump case. For example, in Japanese Utility Model Laid Open No. 60095/88, cooling water which is fed to the outer peripheral portion of the impeller by virtue of centrifugal force created by rotation of the impeller is discharged directly from the discharge port.
However, certain vehicle body layouts may not permit formation of the discharge port at the outer peripheral portion of the impeller. Therefore, the discharge port must be formed at a position offset in the axial direction of the pump from the outer peripheral portion of the impeller. An example of such a case is shown in FIG. 9.
FIG. 9 is a vertical sectional view of a water pump 101. The water pump 101 has a pump case including a pump body 102 and a pump cover 103.
The pump body 102 has a cylindrical portion 102a which supports a pump shaft 106 rotatably through a bearing 105. A bowl-like portion 102b is expanded radially from an end of the cylindrical portion 102a so as to cover about half of an impeller 107 which is fitted on an end portion of the pump shaft 106.
The pump cover 103 is brought into abutment with the bowl-like portion 102b of the pump body 102 through mating surfaces of the two to cover the remaining half of the impeller 107. The pump cover 103 has a suction port 103a formed toward the center of the impeller 107, and a discharge port 103b formed at a position offset in the axial direction of the pump from the outer peripheral portion of the impeller 107.
When the pump shaft 106 is rotated by operation of an internal combustion engine (not shown), the impeller 107 rotates together with the pump shaft 106, whereby cooling water is sucked into the central portion of the impeller 107 through the suction port 103a. The cooling water is then directed to the outer peripheral portion of the impeller 107 by. virtue of centrifugal force generated due to rotation of the impeller 107. The cooling water then passes through a passageway 108 which is bent approximately at a right angle. Thereafter, the cooling water travels to the discharge port 103b located at the offset position, and is then discharged.
In the conventional water pump where the discharge port is located at a position offset in the axial direction of the pump from the outer peripheral portion of the impeller, as mentioned above, the passageway 108 causes the flow of cooling water to bend at a right angle in the area from the outer peripheral portion of the impeller 107 up to the discharge port 103b. Consequently, the cooling water directed to the outer peripheral portion of the impeller 107 by the centrifugal force of the impeller is bent abruptly in the axial direction of the pump, so that the flow in the passageway 108 is disturbed and is not smoothly transported to the discharge port 103b.